Circuits and methods for correcting DC bias and suppressing optical carrier frequency in electro-optic modulators

A circuit, comprising:

• a substrate comprising:
• an input receiving an optical carrier having a frequency;
• and
• a waveguide splitting the input into a signal path having a signal path output and a control path having a control path output;
• a first electro-optic modulator (EOM) comprising a signal path radio frequency (RF) signal structure comprising electrodes disposed along the signal path and configured to receive voltages to impose an RF signal on the optical carrier in the signal path;
• a signal path carrier suppression structure comprising electrodes disposed along the signal path;
• a second EOM comprising a control path RF signal structure comprising electrodes disposed along the control path;
• a control path carrier suppression structure comprising electrodes disposed along the control path;
• a photodetector coupled to the control path output;
• and
• a controller comprising circuitry configured to:
• determine a carrier suppression voltage for the control path using changes in optical intensity at the photodiode caused by applying voltages to the electrodes of the control path carrier suppression structure;
• and
• suppress the frequency of the optical carrier at the signal path output by applying the carrier suppression voltage to the electrodes of the signal path carrier suppression structure.

A method, comprising:

• determining a DC bias voltage for a control path using a control path DC bias structure;
• correcting DC bias in a signal path by applying the DC bias voltage, or a function thereof, to a signal path DC bias structure;
• operating a signal path radio-frequency (RF) signal structure and a control path RF signal structure for a time period during which DC biases in the signal path and in the control path drift;
• determining an updated DC bias voltage for the control path using the control path DC bias structure;
• and
• correcting the drift of the DC bias in the signal path by applying the updated DC bias voltage, or a function thereof, to the signal path DC bias structure.

A method, comprising:

• determining a carrier suppression voltage for a control path using a control path carrier suppression structure;
• suppressing a carrier frequency at a signal path output by applying the carrier suppression voltage, or a function thereof, to a signal path carrier suppression structure;
• operating a signal path radio-frequency (RF) signal structure for a time period during which the carrier frequency changes or carrier suppression voltages in the signal path or in the control path otherwise drift;
• determining an updated carrier suppression voltage for the control path using the control path carrier suppression structure;
• and
• suppressing the carrier frequency at the signal path output by applying the updated carrier suppression voltage, or a function thereof, to the signal path carrier suppression structure.

A method, comprising:

• determining a DC bias voltage for a control path using a control path DC bias structure;
• correcting DC bias in a signal path by applying the DC bias voltage, or a function thereof, to a signal path DC bias structure;
• determining a carrier suppression voltage for the control path using a control path carrier suppression structure;
• suppressing a carrier frequency at a signal path output by applying the carrier suppression voltage, or a function thereof, to a signal path carrier suppression structure;
• determining an updated DC bias voltage for the control path using the control path DC bias structure;
• correcting the DC bias in the signal path by applying the updated DC bias voltage, or a function thereof, to the signal path DC bias structure;
• determining an updated carrier suppression voltage for the control path using the control path carrier suppression structure;
• and
• suppressing the carrier frequency at the signal path output by applying the updated carrier suppression voltage, or a function thereof, to the signal path carrier suppression structure.